The background description set out below represents a background description for the invention and therefore need not necessarily represent prior art.
Vehicles in general and at least to some extent heavy vehicles in particular are the focus of ongoing development with a view to fuel efficiency and reduced exhaust emissions. Such factors as growing official concern about pollution and air quality, e.g. in urban areas, have led to the adoption of emission standards and rules in many jurisdictions.
In operating heavy vehicles such as trucks, buses and the like, vehicle economy has over time also had an ever increasing impact on the profitability of the activity in which they are used. Apart from the procurement cost of a vehicle, the main expense items for its routine operation are pay for the driver, repair and maintenance costs and fuel for its propulsion. It is therefore important to try as far as possible to reduce costs in each of these areas.
One area in which development is at least partly stimulated by an endeavour to reduce emissions and fuel costs is that of hybrid vehicles. Hybrid vehicles use two or more sources of power output and/or fuel, and one usual type of such vehicles is the electric hybrid vehicle, in which one or more electrical machines may be used to generate force which acts upon the vehicle's tractive wheels.
The electrical machine affords the advantage of making it possible for electrical energy to be converted to propulsive force with a relatively high degree of efficiency by the electrical machine, which at the same time may also be used to apply braking force to the vehicle's tractive wheels and thereby use the kinetic energy absorbed from them to regenerate electrical energy for feeding back to the vehicle's electrical system and in particular to an energy store. The regenerated energy may subsequently be reused by the electrical machine to generate propulsive force.
Hybrid vehicles thus provide a way of reducing fuel consumption, but it is also very important that they be operated in an economical way by their drivers, since the way a vehicle is operated may have a very large impact on overall fuel economy. This has led to the development of systems intended for example to make it easier for drivers and owners to assess whether vehicles are actually being operated in a fuel economising way.
However, the most advantageous way for a vehicle such as a hybrid vehicle to be operated, e.g. from a fuel economy perspective, is not always obvious to its driver.